JPS5818686B2 - converter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to a device for generating an electrical representation of the instantaneous amount of deflection or vibration of a piezoelectric curved body or bimorph, and more particularly of a deflectable bimorph.

A typical piezoelectric bimorph has a pair of electrically polarized piezoelectric ceramic elements coupled to opposite sides of a common substrate.

The bimorph U can be curved or deflected by fixing one end, allowing the other end to bend freely, and applying an appropriate voltage between each piezoelectric ceramic element and the substrate.

In this mode of operation, the bimorph is said to act as a motor.

The amount and direction of deflection of the bimorph can be controlled by changing the polarity and magnitude of the applied voltage.

The bimorph's ability to deflect in response to applied signals is useful in a variety of applications.

One such application is in video tape recorders.

Such video tape recorders have a playback or readout transducer attached to one end of a deflectable bimonuf.

A read transducer is physically connected to the video tape and senses, or reads, information recorded in discrete tracks on the tape.

In such devices, it is important that the read transducer is centered on the track in order to accurately sense the track O information.

To ensure that the transducer is properly aligned with the track, its position relative to the center of the track is sensed;
A correction signal is generated and applied to the bimorph to deflect it and the read transducer toward the center of the track.

Although bimorphs are commonly applied in such applications, care is taken to limit or dampen undesirable mechanically induced vibrations in the frequency range of about 10 Hz to 700 Hz. There must be.

Mechanically induced bimorph oscillations result from rapidly bringing the readout transducer into and out of contact with the videotape.

In a helical videotape recorder, the readout transducer briefly loses contact with the tape at the end of each track;
Then start reading the fire track and immediately come into contact with the tape.

The transducer comes into contact with the tape and then separates from it. As the readout transducer receives a mechanical impulse, it causes it and the bimorph to vibrate.

It is well known that such vibrations can be limited by so-called dead rubber pads mounted on either side of the transducer to absorb impulses from the transducer without direct rebound.

However, such pads also limit the range over which the bimorph can deflect, thus limiting the dynamic deflection range of the transducer.

Furthermore, such a pad may be a helical video tape recorder in which the transducer head structure rotates at high speed.

When used as a pad, the pad experiences accelerations approaching or exceeding 10005'.

At this level, it is difficult to ensure that the pad stays in the intended position.

Vibrations in the readout transducer are generated not only by mechanical impulses but also by electrical pulses.

For example, in a videotape recorder, slow motion and other effects can be generated when playing video; half-speed slow motion of the tape slows down the cheap speed to minus the normal speed and causes the readout transducer to slow down each track before proceeding to the next track. This can be generated by reading the track twice.

In order to read a track twice, the read transducer must be physically repositioned or reset at the beginning of the track to be repeated.

This read transducer glue setting is accomplished by applying an electrical reset signal to the deflectable bimorph on which the read transducer is mounted and deflecting the bimorph and transducer to reset the transducer to the beginning of the desired track. .

The reset signal is an electrical pulse that causes the bimorph to oscillate, and as previously discussed, such oscillations must be damped or damped g-tr to ensure proper alignment between the read transducer and the videotape.

Dead rubber dampens electrically induced vibrations.
Full use of the pads presents the above-mentioned difficulties in damping mechanically induced vibrations.

Therefore, in a videotape recorder having a transducer mounted on a deflectable bimorph, it is desirable to provide means for sensing the vibrations of the bimorph and generating an electrical signal that detects the range of such vibrations.

This electrical signal can be used to generate a damping signal to be applied to the bimorph to damp vibrations.

The advantages of bimorph electrical vibration sensing for use with videotape recorder transducers may be applied to other applications where it is desirable to dampen bimorph vibrations.

It is therefore a general object of the present invention to provide an improved vibration sensor for a deflectable bimorph supporting transducer.

Another object of the present invention is to provide a vibration sensor that is inexpensive, compact, and has good responsiveness to vibrations of a bimorph for supporting a transducer over a wide frequency range.

Yet another object of the invention is to provide a bimorph vibration sensor particularly suitable for videotape transducers.

The present invention relates to a bimorph vibration sensor in the form of a transducer support piezoelectric generator combined with a piezoelectric motor element that senses the vibrations of the transducer support motor element and generates an electrical signal that reflects the vibrations.

In one embodiment, the transducer supporting piezoelectric generator and motor are mounted on a common substrate and fixed at one end so that deflection or vibration at the other end changes the instantaneous degree of deflection of the motor element and the supported transducer. A piezoelectric generator generates an electrical signal indicating .

The piezoelectric motor/generator combination preferably comprises a single piezoelectric motor having one side and an opposite side on a tip plate covered with a pair of conductive layers, one layer for the motor and one layer for the generator. Ceramic element straw formed.

The two conductive layers are separated by a dielectric gap to electrically isolate the piezoelectric generator from the signal applied to the piezoelectric motor.

From the following description, it will become clear that the present invention can be applied in various ways and can be particularly preferably used in helical VTRs.

Therefore, although embodiments of the invention are illustrated and described with particular reference to helical VTRs, it is to be understood that the scope of the invention is not to be limited to such helical VTRs.

In order to more clearly describe the present invention and the combination of the present invention with other inventions that can be used in helical VTRs, the following description includes not only embodiments of the present invention, but also other inventions not claimed in the claims. It also covers examples.

Other such inventions include U.S. Patent Application No. 66,865.
There are No. 3 and No. 668580.

As mentioned above, some of the embodiments described herein relate to helical VTRs.

The embodiments particularly relate to a method and apparatus for controlling the alignment of a read transducer with respect to a track on a videotape.

Therefore, a brief description of the operation of a VTR read converter is given next.

In the figures, particularly in Figure 1, a scanning drum 20 of a helical VTR is shown.
is shown having a rotatable portion supporting a reproduction or "read" head that contacts and scans successive tracks on a magnetic video tape.

The scanning drum 20 has a pair of drum sections 22 and 24 around which a video tape 26 is wound.The tape 26 is moved in the direction of arrow A by a tape transport means (not shown) and is moved along a helical path. with drum parts 22 and 24
wrapped around.

Tape 26 is maintained in tight contact with and in alignment with the drum by guide rollers 28 and 30 and the tension applied to the tape by the tape feeder.

In a helical VTR, the information tracks run diagonally with respect to the length of the tape, and a portion of one such track 32 is shown in FIG. 1, enlarged in size for clarity.

In order to sense the information recorded on the track 32, the read transducer head 34 rotates the drum portion 2 in the direction of arrow B.
It is attached to 2.

The movement of the tape 26 and the rotation of the transducer 34
is brought into contact with the tape along track 32 and generates an electrical signal representative of the information previously recorded on that track.

This electrical signal is provided to a signal processing circuit for processing in a manner well known in the art.

The extent to which transducer 34 can faithfully reproduce all of the information previously recorded on track 32 depends on whether transducer 34 accurately tracks track 32.

Tracking problems arise, for example, when a videotape or track becomes degraded by temperature or humidity induced dimensional changes in the tape or by problems with a tensioning mechanism such as a chive drive system.

Due to such tracking issues, track 32
It is desired to sense the instantaneous position of transducer 34 with respect to.

An apparatus for sensing the position of a read transducer relative to a track is disclosed in US Patent Application No. 6,685,71.

Briefly, if perfect tracking between the read transducer and the track has not occurred, an electrical correction signal is applied to the deflectable support arm, such as a bimorph, on which the read transducer is mounted.

This correction signal causes the support arm to deflect the transducer toward the track center to reduce tracking errors.

Deflection of the readout transducer is also preferred in helical 'VTRs, such as those described in US Pat. No. 6,686,52.

In such VTRs, slow motion and other effects of the played video footage are generated, such as a half speed slow motion effect where the speed of the tape advance system is reduced to half its normal speed and the readout transducer cuts each track into two. It is produced by making it appear one after another.

In order to read a track twice, the read transducer must be physically repositioned or reset at the beginning of the track to be repeated.

This resetting of the readout transducer is described in U.S. Patent Application No. 668
In one embodiment of the VTR disclosed in US Pat. This is accomplished by deflecting the support arm and transducer.

The reset signal is a cedar of electrical pulses that attempt to cause the support arm to vibrate or oscillate; such vibrations are damped to ensure proper alignment between the transducer and the tape.

As the transducer moves in and out of contact with the tape, it also causes vibrations in the deflectable transducer support arm.

For example, in the scanning drum configuration of FIG. 1, read transducer 34 experiences dropout because it loses contact with tape 26 in the gap between guide rollers 28 and 30 during each rotation of drum 20.

Contact between transducer 34 and tape 26 is reestablished when transducer 34 passes roller 28 as it rotates in direction B.

Vibrations imparted to the deflectable transducer support arm are of course undesirable since such vibrations result in tracking losses.

This tracking loss due to vibrations can be minimized or eliminated by sensing the fluctuations of the deflectable support arm and providing a damping signal to the support arm to dampen the vibrations.

In a helical VTR where it is desired to include a deflectable support arm to reduce tracking errors, including means for damping electrically and mechanically induced vibrations of the deflectable support arm. is also desired.

Preferably, damping the vibrations can be done electronically, in which case some means is required for sensing the amplitude of the vibrations and generating an electrical signal representative thereof.

A deflectable readout transducer assembly including means for sensing all induced vibrations is shown in FIG.
6 is generally indicated.

A read transducer 34 is provided at one end of the assembly 36.

Its output is connected via line 38 to a pair of transducer output terminals 40.

From these terminals the converter output is routed to video processing circuit 84 on line 8.
2.

Support arm 42 for holding and deflecting transducer 34
is a piezoelectric bimorph that deflects or bends when a deflection potential is applied to it.

The bimorph is formed from a number of layers coupled together to act as a "piezoelectric motor" 43 and includes a top piezoceramic element or layer 44 and a bottom piezoceramic element or layer 46.

The various layers of transducer assembly 36 are more clearly shown in FIG. 2a.

Piezoceramic elements 44 and 46//'i are coupled together to a common conductive substrate 48.

Substrate 48 limits the movement of the bimorph to a bending motion in response to an applied potential.

Conductive layers 50 and 52 cover the outer surfaces of elements 44 and 46 to apply a potential to all piezoceramic elements 44 and 46.

Terminals 54 and 56 (FIG. 2) are electrically connected to layers 50 and 52, respectively, for receiving deflection potentials.

Substrate 48 also has an input terminal 58 to serve as electrical common for an applied deflection potential.

A potential to deflect support arm 42 is applied to piezoceramic element 44 between terminals 54 and 58 and piezoceramic element 46 between terminals 56 and 58.

To deflect the support arm 42 with the free end 46 fitted with the transducer 34, the arm 42 is fitted with a spacer 6, which may be held in place by a bolt (not shown) passing through a hole 66.
Cantilevered between 4 spaces.

In operation, appropriate deflection potentials are applied to piezoceramic elements 44 and 46 via input terminals 54, 56 and 58.

At this time, support arm 42 bends at its free end 60, deflecting transducer 34 in a direction and degree that depends on the magnitude and polarity of the potentials applied to terminals 54, 56, and 58.

In some applications, piezoelectric motors need to include only one piezoceramic element coupled to a substrate.

For example, a single piezoceramic element may have a bottom surface bonded to a conductive substrate and a top surface covered by a conductive layer that causes the element to bend when an electrical potential is applied between the substrate and the conductive layer.

However, if a large amount of deflection is required in such a VTR, a motor element consisting of two piezo ceramic elements 44 and 46 as shown in FIG. 2 is preferred.

In addition to including a piezoelectric motor 43 for deflecting the transducer 34, the assembly 36 may include a deflection or vibration sensor in the form of a piezoelectric generator.

Generator 68, in the illustrated embodiment, has end portion 10 of piezoceramic element 44 coupled to substrate 48 as described above.

However, generator 68 can be formed by a centrally located portion of element 44.

The generator has a separate electrically conductive layer 72f over the component portion 70.

Conductive layer 72 includes a dielectric gap 74 to electrically isolate the output of generator 68 from the potential applied to conductive layer 50.
It is insulated from the conductive layer 50 by.

Generator 68 is cantilevered at 76 and has opposing deflectable free ends 78 .

Therefore, by electrical or mechanical impulses the motor 43
When a vibration or deflection occurs in the generator element 68 , a corresponding deflection or vibration of the free end 78 of the generator element 68 occurs, which increases the instantaneous amount of deflection of the motor 43 and the transformer 34 between the common substrate 48 and the conductive layer 72 . produces an electrical signal representing the

In the above description of piezoelectric motors and generators, 1
Generator 68 is piezoceramic element portion 7 of element 44
0 and motor 43 includes the bulk of a piezoceramic element 44.

As shown in FIGS. 2 and 2a, piezoceramic element portion 70 is preferably part of an integral piezoceramic layer or element 44. As shown in FIGS.

However, there is no need for portion 10 to be part of a larger unitary entity.

For example, gap 14 cuts through layer 44 to separate elements 7.
It can be extended backwards to form a zero.

However, even with large amplitude deflection signals applied to elements 44 and 46, these deflection signals.

It has been found that if the element portion 70 is part 2 of a larger integral element 44, then substantially no contribution is made to the generator 68.

However, cutting the element down to the ground plane increases the motor-to-generator isolation and increases the susceptibility of the element to surface contamination.

A vibration sensor that generates an electrical output indicative of fluctuations in the two arms 42 has a frequency of approximately 10 Hz to at least 400 H2 (at which frequencies the bimorph support arms shown have a resonant frequency).

) must respond to vibrations over a frequency range extending up to

The generator 68 of FIG. 52 exhibits good frequency response over the desired range.

This response will be better than the frequency response of the generator, which may extend transversely to the length of the support arm 42, especially at lower frequencies.

Preferred dimensions for support arm 42 are approximately 0.9 inches in length extending from free end 60 to cantilever point 76 and approximately 0.5 inches in width W.

Each of layers 44, 46 and 48 preferably has a thickness of about 0
．． 0.006 inches thick, and conductive layers 50, 52 and 1
2 has a thickness in the range of several microns.

The width of conductive layer 12 is preferably about 50 mils, measured between gap 74 and the nearest end of support arm 36.

Substrate 48 is preferably made of brass and includes conductive layer 50.
52 and 12 are nickel adhesion bodies.

Piezoceramic layers 44 and 46 are bonded to substrate 48, such as by epoxy adhesive.

Read transducer assembly 36 may be enclosed within a housing (not shown) having a top and bottom portion that holds assembly 36 therebetween.

The entire housing assembly can be held together by bolts passing through holes 66 (FIG. 2) and appropriate holes in the top of the housing.

A more detailed description of a housing that can be used for assembly 36 is provided in the above-mentioned U.S. Patent Application No. 66,865.
It is given in No. 1.

The piezoelectric motor and generator assembly described above is a low cost and reliable device that can be controllably deflected to instantaneously produce an output signal representative of a controlled deflection or vibration induced deflection.

It is particularly used as part of a readout transducer assembly for a VTR and is illustrated schematically in connection with the VTR described below.

The piezoelectric motor/generator combination described above for momentarily deflecting a readout transducer and sensing its vibrations is used in an electronic feedback control system to damp the vibrations of a videotape readout transducer.

Transducer damping means are provided using so-called dead rubber pads to absorb transducer vibrations, but these pads also limit the effective deflection range of the transducer.

If the pads are mounted on the read head in close proximity to the transducer of a rotatable scanning drive, they will experience large i-forces as the drum rotates.

Under these conditions, it becomes difficult to properly position and hold the pad on the drum.

An improved damping system in which the motor/generator combination described above may be used is shown schematically in FIG.

However, before describing this improved damping system, a brief description of the associated transducer circuitry is given to clearly demonstrate how the damping system cooperates with the associated circuitry.

In FIG. 3, read transducer 34 operates as described above to sense or read information previously recorded on a videotape track. is part of assembly 36 and provides a deflection signal for correcting alignment of transducer 34 with one track or resetting transducer 34 to the beginning of one track in a slow motion mode of operation as described above. It has a deflectable support arm 42 for deflecting the transducer 34 accordingly.

Support arm 42 is cantilevered at point 76 and transducer 34
The opposite end portion supporting the is free to deflect.

The electrical signal output of transducer 34 is provided on conductor 82, e.g.
A video processing circuit 84 is provided for generating a composite television TV signal for RF transmission.

The output of transducer 34 is also provided to transducer position control circuit 86.

The functionality of control circuit 86 is described in US patent application Ser. No. 6,686, and is not part of the present invention.

However, simply stated, the position control circuit 86 provides a constant frequency "oscillation" signal that is applied to the deflectable support arm 42 to deflect or "oscillate" the transducer 34 back and forth across a track at a constant speed. Occur.

Because the "oscillations" cause the transducer 34 to move laterally with respect to the track, the signal output of the transducer 34 will be amplitude modulated at the "oscillation" frequency.

The envelope of this amplitude modulated signal contains information regarding the alignment between the transducer 34 and the track being read, which is detected and produces a correction signal to move the transducer 34 feet toward the center of the track.

This correction signal and a "vibration" signal appear on conductor 88 and are applied to deflectable support arm 42.

A transducer reset signal generator 90 produces an electrical signal that is applied to the deflectable support arm 42 to selectively reset the transducer 34 to the beginning of the track as required.

A circuit for generating such a reset signal is the subject of US Pat. No. 6,686,652.

A reset signal from signal generator 90 and a "vibration" correction signal from circuit 86 are provided to frequency compensator 92 .

The device 92 includes an amplifier whose frequency response is complementary to undesired residual response variations of the support arm 42 when electronic feedback control damping is applied as schematically illustrated in FIG. .

Frequency compensator 92 increases the effectiveness of the electronic damping circuit to provide the desired uniform frequency response for the entire system.

The region of increase is between 300 and 400 Hz, where the electronic damping action is applied to the arm 42 at its primary mechanical resonance frequency.
does not completely eliminate the frequency response increase.

The frequency compensated deflection signal from compensator 92 is provided via conductor 94 to summing amplifier 96 .

This amplifier 96 adds the deflection signal to the transducer damping signal produced by the feedback loop described below.

The output of the summing amplifier 96 is connected to the driving amplifier 1 via a conductor 98.
00 is given.

This amplifies and applies its input to the deflectable support arm 42 to deflect the transducer 34 to the center of the track in a controlled manner and to maintain the appropriate transducer in track alignment.

Various deflection signals applied to support arm 42, particularly those generated by reset generator 90, can cause unwanted vibrations of arm 42.

This is especially true if the poom 42 is a bimorph, since the bimorph exhibits resonant characteristics that tend to drive it into damped oscillation.

To dampen such oscillations, a negative feedback loop is included in the system shown in FIG.
to damp the vibration or oscillation.

The required damping signal is typically provided by a signal generator that generates a deflection velocity signal representative of the instantaneous deflection velocity of readout transducer 34.

In the embodiment shown in FIG. 3, the signal generator includes a sensor 102 integral to support arm 42, which sensor 102 generates a signal representative of the instantaneous deflection position of transducer 34.

Additionally, a differentiator 104 is included to convert the transducer position signal to a transducer velocity signal.

Sensor 102 is preferably a piezoelectric generator of the type shown in FIG. 2 integrally formed with the bimorph support arm.

The output of sensor 102 is provided to a high input impedance amplifier 106 that provides little loading to sensor 102.

Since sensor 102Fi, curvature-wise, is equivalent to a voltage source in series with one capacitor, the electrical load on sensor 102 should be small to effectively couple the low frequency signals from sensor 102. There must be.

The output of amplifier 106 is provided to adder 108.

The other input of adder 10B will be described later. Furthermore. It is then applied to differentiator 104.

It differentiates the transducer position signal from sensor 102 and converts the position signal into a signal representative of instantaneous transducer velocity.

Differentiator 104 is shown to have an amplitude versus frequency characteristic similar to a high-pass filter, and thus causes a phase lead in the passed signal.

The significance of the phase shift experienced by the signal passing through the feedback loop will be discussed below to provide a better understanding of the function of the remaining elements of the feedback loop.

The support arm 42 is preferably a piezoelectric bimorph so that it exhibits the well-known first-order and anti-resonance characteristics of piezo crystals, as well as higher-order resonance characteristics.

FIG. 4a shows the combined frequency response of a bimorph motor/generator combination of the type shown in FIG.

This response was determined by applying a variable frequency, constant amplitude sine wave to the piezo electric motor and measuring the combined output of the piezo generator.

Therefore, it is generated.

The results of such measurements are shown in Figure 4a, which
It shows a resonance point near 00 Hz and an anti-resonance point varying from about 700 Hz to about 1000 Hz depending on the particular bimorph used.

The maximum amount of force in the motor/generator combination is generated at the resonant position,
Minimum output occurs at very low frequencies and anti-resonant positions.

Higher order resonance characteristics are not shown in Figure 4a.

Since the output of the motor/generator combination is maximum at the resonant position, vibrations or oscillations will occur at its resonant frequency when the bimorph is excited by an electrical or mechanical impulse.

Therefore, to reduce the possibility of such oscillations, the feedback loop is made to have a bimorph damping signal that is 180° out of phase with respect to the signal that originally excited the bimorph into oscillation, thereby; to the non-oscillating direction.

To ensure that the damping signal is in the correct phase,
The phase response of the bimorph motor/generator combination is considered.

As shown in Figure 4b (with curve J labeled Bimorph Response), the signal near the resonance position (approximately 400
Hz) undergoes a phase shift of approximately 90° as it passes through the motor/generator combination, and the high frequency signal undergoes a 180° phase shift.

In order to ensure that the signals near the resonance location undergo a net phase shift of 180° around the feedback loop, and all signals within the loop are inverting the feedback amplifier before being applied to the support arm 42. To be phase shifted by 180 degrees, the signals near resonance must be phase compensated by 90 degrees so that their net phase shift is zero at the input to the inverting feedback amplifier.

This prevents the loop from oscillating at the resonant frequency due to instability in the feedback system.

Since signals with frequencies far from the resonance location have very small amplitudes, the loop gain of the feedback loop is always less than unity so that the phase shift that these signals undergo does not cause instability in the reel width.

In the feedback loop of FIG. 3, the transducer velocity signal produced by differentiator 104 is provided to low pass filter 110.

The cutoff frequency is chosen to substantially reduce signals contributing to the bimorph's second and higher order resonance characteristics.

Such a signal must: - have a frequency greater than or equal to 2000 Hz, and be filtered by filter 110 at least 20
It is attenuated in dB (decibels).

Filter 110 imparts a certain phase delay to the signal passing through it and provides an initial phase delay of 90 DEG (see FIG. 4) tl-by the pi self itself.

To compensate for the total phase delay experienced by signals near resonance, a phase advance circuit 112 is provided after filter 110, which phase shifts the signal from filter 110 so that signals with frequencies near resonance are advanced. There will be a net phase shift of 00 upon exiting circuit 112.

"Response by curve advance circuit 112" in FIG. 4b shows the action of advance circuit 112.

In effect, the differentiator 104 also adds some phase lead, thereby assisting the lead circuit 112 in properly adjusting the phase of the signal near the resonance location.

The signal from lead circuit 112 near the resonance location has a phase of OO with respect to the signal that initially excites the bimorph and is provided to negative feedback amplifier 114 which inverts the signal from lead circuit 112.

The output of amplifier 114 is summed with the transducer deflection signal from conductor 94 in adder 96 and amplified in drive amplifier 100;
It is applied to bimorph support arm 42 to damp or dampen its vibrations.

Feedback amplifier 114 has a variable amount of negative feedback to adjust the gain of the feedback loop to accommodate differences between bimorphs.

The feedback loop shown in FIG. 3 includes means for compensating for various anti-resonant responses between the bimorphs.

The frequency response curve is shown as a solid line in FIG. 4a, and the dotted line is the variable nature of the anti-resonance characteristics between the various bimorphs.

For example, at 700 Hz, the frequency response of one bimorph is significantly smaller than that of the other bimorph, as shown by the difference between the solid and dotted lines at the 700 Hz frequency.

In FIG. 4b, the phase response of the feedback system with the lead circuit is such that if a signal near 700 Hz with a phase shift of 180° is applied to the inverting feedback amplifier 114, those signals will have the original excitation deflection. If they are applied to the support arm 42 in phase with the signals and their amplitude is sufficiently large at a frequency corresponding to a positive feedback condition for the feedback loop, they will result in a phase lead relative to the oscillation at that frequency.

A bimorph with the frequency response shown by the solid line in Figure 4a has a very small output at 700 Hz, so the overall loop gain of the system for such signals avoids oscillation regardless of their phase response. low enough to do so.

However, the bimorph exhibiting a larger gain at 700 Hz, as shown by the dotted line, introduces instability into the system unless otherwise compensated.

The feedback system in FIG. 3 transfers a portion of the excitation deflection signal to the sensing device
2 outputs to compensate for the above-mentioned differences between the bimorphs by effectively nulling the signal that would normally undergo a 180° phase shift between the signal input to the bimorph 42 and the signal output at the sensor 102. .

A signal undergoing such a 180° phase shift is shown near the anti-resonance position in FIG. 4b.

Therefore, the signal near the anti-resonance location can be effectively nulled out by coupling to the transducer assembly 36 a portion of the signal normally provided thereto.

In FIG. 3, the means for providing a portion of the deflection signal and combining it with the position signal produced by sensor 102 includes a potentiometer (POT) 116 and a summer 108.

The deflection signal produced at the output of adder 96 is transmitted to drive amplifier 100.
and 'POT1.16.

A portion of the deflection signal is provided to summer 108 via conductor 118.

Summer 108 also receives the deflection position signal produced by sensor 102 from amplifier 106 .

The deflection signal (e.g., at a frequency near the anti-resonant position) that undergoes a 180° phase shift in passing through the input to support arm 42 to the output of sensor 102 is zeroed in adder 108 so that the loop is stabilized for frequencies near the anti-resonant position.

This operation effectively creates an artificial null (Hull) near 700 Hz, such that regardless of the bimorph used in the transducer assembly 36, it will have an effective zero near 700 Hz; Ensure that the loop gain for signals is always less than 1 and that the feedback loop is stabilized for signals at these frequencies.

Circuitry for performing the functions of the various blocks of FIG. 3 is shown in FIG.

A transducer deflection signal, including the vibration signal and reset signal described above, is provided to frequency compensator 92 at terminal 120.

Frequency compensator 92 includes a pair of amplifiers 122, 121-.

The frequency response of the compensator 92 is amplified to have a full amplitude that reduces frequencies in the range of 300-400 Hz to compensate for residual frequency-dependent variations in the deflection sensitivity of the support arm 42 after the electronic damping has been done. 122 and amplifiers 122 and 124.

The output of amplifier 124 is connected to summing amplifier 96 via conductor 94.
given to.

Summing amplifier 96 also receives input from the feedback control loop at its non-inverting input.

The output of summing amplifier 9.6 is provided via conductor 98 to drive amplifier 100.

The negative return loop begins at terminal 126 to which the output from sensor 102 is applied.

The signal from sensor 102 is provided to an amplifier.

This is a frequency compensated feedback amplifier 128.

The output of amplifier 128 is applied to the inverting terminal of summing amplifier 108, which in turn applies to the same input the transducer deflection signal to create an artificial zero at the anti-resonant position as described above. receive some.

Diode 131 connects sensor 102 and support arm 42
Amplifier 121 protects against high transient voltages due to accidental short circuits between inputs to the amplifier 121.

The output of summing amplifier 108 is provided to differentiator 104.

This is a series connection of capacitor 129 and resistor 130)
It will be.

The low-pass filter 110 receiving the output of the differentiator 104 has 13
6 is an active elliptical filter consisting of amplifiers 132 and 134.

Advance circuit 112 receives the output of filter 110 and consists of a capacitor 136 and a resistor 138 connected in series.

This output is applied to the inverting input of feedback amplifier 114 whose feedback and therefore forward gain is adjusted by varying variable resistor 140.

The output of amplifier 114 is applied to the non-inverting input of summing amplifier 96 and then to drive amplifier 100 via conductor 98, which is then deflected to deflect transducer 34 in the manner described above. 1 drive the possible support arm 42.

The damping system described above provides improved damping for deflectable videotape transducers without limiting their dynamic range.

The feedback control loop, in combination with a motor-generator converter, provides a reliable and low-cost solution for VTRs and other applications where the vibrations of deflectable bimorph conversion assemblies require damping. Provides a vibration damper.

From the foregoing, it is believed that it is understood how a videotape read transducer can be controllably deflected and attenuated to maintain alignment between itself and the tape track.

An improved bimorph transducer scheme is now described that includes a method of providing a deflection signal to a deflectable bimorph to achieve maximum deflection sensitivity.

Such a change. A successful scheme can be used in the VTR described above and is illustrated for its application.

However, if the deflectable bimorph described below is
The improved method of driving can also be used in other methods where it is desired to achieve large bimorph deflections.

Bimorphs used for bidirectional deflection are generally constructed from two layers of piezoceramic material bonded to opposite sides of a conductive substrate.

One end of the bimorph is cantilevered, and the other end is free to be deflected in response to a voltage applied to the bimorph.

The direction in which the bimorph is deflected depends on the polarity of the voltage applied to it and the polar direction (poli
ng direction).

The polarization direction of the piezoceramic element is set by initially directing a unidirectional electric field that totally polarizes the element according to the field direction.

A polarized piezoceramic element is then said to have a "polarization direction" and then exhibits unique mechanical properties when subjected to a subsequently applied voltage.

A known method for deflecting or bending a bimorph is the sixth method.
Illustrated in the figure is a bimorph 142 with piezoceramic elements 14 coupled to opposite sides of a conductive substrate 148.
4 and 146.

Bimorph 142 is cantilevered at 150 while its opposite end 152 is free to deflect.

Piezoceramic elements 144 and 146 are each shown with arrows indicating their respective polarization directions.

When they are aligned as shown in FIG. 6 with the arrows pointing in the same direction, they are said to have a common polarization direction.

The polarization directions shown are obtained by applying voltages across the piezo-ceramic elements such that a rising positive potential is applied behind the arrow and a rising negative potential is applied in front of the arrow.

For example, in FIG. 6, bimorph 142 has elements 144,
It is deflected upward by a voltage source 154 connected between 146 and substrate 148.

The polarity of voltage source 154 is such that it applies a voltage to element 144 in the same direction as its original polarization voltage, whereas voltage source 154 applies a voltage of opposite polarity to its original polarization voltage. is applied to element 146.

If the polarity of the deflection voltage applied to a piezoceramic element is the same as the polarity of the element's original polarization voltage, the applied deflection voltage is referred to herein as being applied in the polarization direction.

Thus, voltage source 154 is applied to element 144 in one direction of polarization and to element 144 in the opposite polarity to its direction of polarization.
46.

A pair of piezoceramic elements are aligned and cantilevered as shown in FIG.

The i-bimorph is bent in the direction of the element being driven in its polarization direction.

Thus, bimorph 142 is bent upwardly toward element 144 when driven by voltage source 154 having the indicated polarity.

If no voltage is applied to the bimorph, no deflection i will occur.

When voltage source 156 is connected between substrate 148 and elements 144 and 146 as shown in FIG.
is driven by 1 in its polarization direction, and the bimorph 142 is deflected downward as shown.

For some reason, the method of driving the bimorph shown in FIG. 6, in which the deflection voltage is applied in the direction of polarization of one piezoceramic element and opposite to the direction of polarization of the second piezoceramic element.

) is satisfied.

However, if large deflections are required, large deflection voltages are required as well.

Applying a large voltage in the direction opposite to the polarization direction of a piezoceramic element depolarizes the element.
ize) to reduce its ability to bend or deflect.

A method of driving a bimorph with a large amplitude deflection voltage without depolarizing any piezoceramic elements is shown in FIG.

In this improved method, bimorph 158 includes a pair of electrically polarized piezoceramic elements 160 and 162 that are also aligned in a common polarization direction and coupled to a common substrate 1164 therebetween. are doing.

Bimorph 158 is cantilevered at one end 158 and freely deflectable at opposite end 168.

In this improved method of deflecting the bimorph, the deflection voltage is such that the polarity of the applied voltage is always in the direction of polarization of the element (in that direction, a large deflection of the bimorph can occur without depolarizing any piezoceramic element). A voltage is applied as shown in FIG.

) is given to the piezo ceramic element so that

Ru.

As shown in FIG. 1, when bimorph 158 is deflected upwardly, voltage source 110 is connected between piezoceramic element 160 and substrate 164 such that the polarity of the applied voltage is The polarization should be in the ′ direction.

No voltage of opposite polarity is applied to element 162 since most of the bending of the bimorph is caused by the element being driven in its polarization direction.

When bimorph 158 is deflected downward.

In this case, a voltage source 172 is connected between the element 162 and the substrate 164, and the polarity of the applied voltage is in the polarization direction of the element 162.

No voltage of opposite polarity is applied to element 160.

If bimorph 168 remains undeflected,
Equal magnitude voltage sources 170 and 172 are applied between elements 160 and 162 and substrate 164 such that both piezoceramic elements 160 and 162 are aligned in their polarization direction.
Driven.

No deflection occurs as a result of driving the pixel elements equally.

Although voltage sources 170 and 172 are shown as constant amplitude voltage sources, this need not be the case.

Bimorph 158f: When deflecting up and down with a variable amount of deflection, the single YL sources 170 and 172 can be made variable to allow such movement.

However, the polarity of the voltage applied to elements 160 and 162 must always be in the direction of polarization of the element applying the voltage.

The method of varying the magnitude and frequency of bimorph deflection is outlined in Figure 8a.

As shown, a DC voltage from power supply 174 is applied to element 160 in its polarization direction.

Element 162 receives a DC voltage from power supply 176 in the direction of its polarization.

Preferably, power supplies 174 and 176 generate positive and negative DC voltages of magnitude equal to %Vmax.

where Vmax is the peak-to-peak amplitude of the maximum deflection signal applied to elements 160 and 162.

Therefore, with elements 160 and 162 by 2Vmax reversely biased and no other deflection voltages present, no deflection of bimorph 158 will occur.

To effect alternating deflection of the bimorph 158, A
C deflection power supply 118 connects a pair of amplifiers 180 and 182 and D
Coupled between devices 160, 162 and substrate 164 via C power supplies 174 and 176.

The peak-to-peak value of the AC deflection signal applied in phase to elements 160 and 162 will be as large as Vmax without applying a net voltage opposite the polarization direction to either element.

When the deflection signal from power supply 118 varies in a generally sun wave manner, the net voltage appearing across element 160 is shown in Figure 8b.

When cords 160 and 162 are biased in opposite directions at %Vmax and superimposed AC deflection signals are applied to these elements in phase, the net voltage across each of elements 160 and 162 is always It has polarity in the polarization direction.

The curve labeled "deflection" in Figure 8b is for bimorph 1.
58 deflects at twice the instantaneous value of the AC deflection voltage provided by voltage source 178.

When the net voltage across element 160 is a positive value greater than (or less than) %Vmax, the net magnitude of the voltage across element 162 is correspondingly less than (or greater than) a negative value.

However, because of the bias provided by voltage source 176, the net voltage on element 162 will always be in the direction of its polarization unless the magnitude of the AC deflection voltage exceeds Vmax.

The scheme shown in FIG. 8a for driving bimorph 158 is fully DC coupled so that bimorph 158 can be driven by voltage source 178 at very low frequencies.

In certain applications where low frequency bimorph deflection is not required, a scheme such as that shown in FIG. 9 can be used.

In the scheme of FIG. 9, only one amplifier 148 is needed to amplify the AC deflection voltage from voltage source 186.

The amplified deflection voltages are provided to elements 160 and 162 via coupling capacitors 186 and 188, respectively.

Separate DC bias power supplies 190 and 1-92, each having an amplitude j% Vmax, bias elements 160 and 162 such that the net voltage on either element is in the direction of its polarization.

In FIG. 8, a DC power source 114 and an amplifier.

180 are surrounded by a dashed triangular line to indicate that they are, in effect, included together in one composite amplifier that amplifies the deflection signal and also provides appropriate biasing.

Similarly, power supplies 176 and 182 may also be combined in a single composite amplifier.

An example of a pair of compound amplifiers for driving a Bashymorph is shown in FIG.

The bimorph being driven in FIG. 10 is part of a readout transducer for use with the VrR shown in FIG.

A transducer assembly 194 is schematically illustrated in FIG.

However, it may be similar to the transducer assembly 36 shown in FIG.

(Piezoceramic generator 68 is not shown as part of transducer assembly 194 for simplicity of illustration.

) Transducer assembly 194 has a top piezoceramic layer 196 and a bottom piezoceramic layer 198 bonded to a grounded common substrate 200°.

The deflection signal is transmitted to the upper and lower conductive layers 202, 204 of the transducer assembly 1.
94.

The piezoceramic elements 196 and 198 are polarized in a common direction as shown by the arrows.

A read transducer 199 is mounted on assembly 194 and adapted to be deflected in the manner described above.

Piezoceramic layer 196 is driven by composite amplifier 206 and piezoceramic layer 198 is driven by composite amplifier 208.

Amplifiers 206 and 208 receive the low level AC deflection signal at input terminal 210, amplify the deflection signal, and combine the kDC bias signals to conductor layers 202 and 20.
Give to 4.

Generally, amplifier 206 includes a first amplification stage formed by a differential transistor pair 212 and 214 and a second amplification stage formed by a differential transistor pair 216 and 218.

The output of the transistor 218 is the constant current source transistor 22
It is taken between 0.

The amplified signal at the collector of transistor 218 is provided to the bases of emitter followers 224, 226;
and output terminal 2 via emitter resistors 228 and 230.
Given to 32.

The signal at terminal 232 is fed back to the base of transistor 214 via feedback resistor 234, causing amplifier 206 to operate as a negative feedback operational amplifier.

The DC bias appearing at output terminal 232 is typically +
1oov, and is determined by resistors 236, 238, feedback resistor 234, and the +200V power supply.

A 200V peak-to-peak AC deflection signal is applied to output terminal 23 without counteracting the polarization polarization of piezoceramic layer 196.
2 can occur.

Transistors 240 and 242 provide short circuit protection for emitter followers 224 and 226, respectively, to limit the output current in the event that terminal 232 becomes grounded.

Amplifier 208 is similar to amplifier 206 and has a voltage of -100V.
An amplified deflection signal is provided at an output terminal 244 superimposed on the DC bias of.

Amplifiers 206 and 208 are similar to drive amplifier 100 of FIG.
Can be used together to provide amplification performed by.

Combined amplifiers 206 and 208 provide a large amplitude AC deflection signal superimposed on a DC bias voltage to drive the deflectable bimorph without depolarizing it, allowing the driven bimorph to maintain its tendency sensitivity. Make sure you don't lose it.

The transducer scheme shown in Figure 10 and the method shown in Figures 8a and 9 provide improved performance for deflectable bimorphs.

The bimorph motor/generator association +! : provides a compact and reliable device for sensing the instantaneous deflection position of a deflectable piezoceramic support arm, for example.

The illustrated embodiment of this apparatus is shown as part of an improved videotape readout assembly for generating an output signal indicative of the deflection position of a readout transducer.

This novel assembly C relates to a readout transducer capable of oscillating upon receiving an electrical or mechanical impulse by producing an output signal that can be converted into a damping signal for damping or damping the transducer vibrations. solve the problem.

Damping of transducer vibrations involves generating a signal indicative of the speed of a trending or vibrating transducer, converting this speed signal to a damping signal, and applying the damping signal to a transducer support arm to dampen the vibration. This is achieved by the above-mentioned feedback control system which dampens.

Various means are included in the damping system to stabilize the feedback control system at frequencies near the resonant and anti-resonant positions of the bimorph motor generator.

This feedback control system is coupled with a novel bimorph-motor-generator transducer assembly to provide effective damping of deflectable videotape readout transducers without constraining the transducer dynamic range. .

Additionally, this electronic damping scheme does not adversely affect speed due to the large glitches that normally occur in video readout systems.

The damping signal and the transducer deflection signal are preferably determined by the method and apparatus, which eliminates the depolarization effects associated with prior methods by ensuring that the applied deflection signal is always in the direction of polarization of the piezoceramic element. Bimorph transducer support arm is provided.

A compound amplifier embodying this improved method receives a large amplitude transducer deflection signal and applies this signal to the bimorph to achieve large bidirectional bimorph deflection without depolarizing the bimorph, thereby reducing the bimorph deflection. Maintain high sensitivity.

The improvements described above are combined in an improved videotape recording system for use with VTRs and particularly for use with helical VTRs.

However, the improvements can be used independently of each other and in applications other than videotape reading systems.

Furthermore, many modifications to the specific embodiments shown and described will occur to those skilled in the art.

[Brief explanation of the drawing]

1 is a perspective view of a portion of a simplified helical VTR, particularly the rotating scanning drum and read head; FIG. 2 is a perspective view of a read transducer assembly for use with the read head of FIG. 1; FIG. 2a is an enlarged cross-sectional view of the layered configuration of the transducer assembly shown in FIG. 2; FIG. Block diagram of the incorporated feedback control system, No. 4
Figures a and 4b are graphical diagrams showing the frequency and phase response of the bimorph transducer assembly used in the control system of Figure 3; Figure 5 is a circuit diagram of the control system shown in Figure 3;
Figure 6 shows the conventional method of deflecting bimorphs, Figure 7
Figure 8 shows an improved method of deflecting bimorphs.
Figure 8a is a diagram illustrating an improved method of varying the direction and magnitude of deflection of a bimorph; Figure 8b is a graphical diagram illustrating the net voltage applied to one element of the bimorph shown in Figure 8a; FIG. 10 shows a deflectable readout conversion embodying the improved bimorph deflection method shown in FIG. 8a. FIG. In the figure, 34,199 is a readout converter, 42,158194
36 is a support arm, 36 is a readout transducer assembly 43 is a piezoelectric motor, 48 is a conductive substrate, and 68 is a piezoelectric generator.

Claims (1)

[Scope of Claims] 1. A deflectable transducer device for use in a magnetic recording/reproducing device, comprising: a piezoceramic motor element coupled to a conductive substrate, one end being cantilevered and a deflectable support arm whose other end is freely deflectable in response to an applied deflection potential. (b) a readout transducer mounted on the free end of the support arm; (c) a readout transducer arrangement comprising a piezoceramic generator coupled to the substrate and deflected together with the motor element to generate an output signal indicative of the instantaneous deflection of the readout transducer; 2. Claim 1, wherein the motor and generator element are composed of an integrated piezoceramic element.
Readout transducer device as described in Section 1. 3. The motor and generator elements have respective bottom and top surfaces, the bottom surfaces of the motor and generator elements are coupled to a common substrate, and each of the top surfaces has a respective bottom surface and a top surface separated by a dielectric gap. 3. Read transducer device according to claim 2, characterized in that it is covered with an electrically conductive layer.